1. Field of the Invention
This invention relates to a head positioning apparatus for tape recording heads and, more particularly, to a fine pitch lead screw and lever arm system that positions a tape head in a tape cartridge back-up drive for personal computer data storage systems.
2. Statement of the Problem
In tape cartridge back-up systems for personal computers, parallel tracks of data are recorded on a tape media in a data cartridge. A recording head with a single read/write gap must be positioned on the tracks such that the head gap centerline is within a prescribed dimensional tolerance of the recorded track centerline. This requires precision in the alignment and positioning of the tape head and in the tracking of the tape head.
The problem of such track positioning has been addressed in other magnetic media devices that require a head to be positioned or repositioned to different tracks located on the media. For example, magnetic disk storage systems use stepper motors with lead screws that directly drive the head or alternatively use a band wrapped around a post in conjunction with a pivoting arm to position a head over the disk shaped media. Lever arms have been used to position the recording head.
In U.S. Pat. No. 4,630,145 for a "Fine Positioning Apparatus for Floppy Disk Drive", issued to Thompson, two stepper motors are used to provide both coarse and fine positioning to a read/write head. The first stepper motor engages a first lead screw that directly moves the head carriage to provide a coarse adjustment. The second stepper motor is connected to a second lead screw which causes the first lead screw and the head carriage to move in fine adjustment. Similar devices are disclosed in U.S. Pat. No. 4,747,004 and in U.S. Pat. No. 4,609,958.
In previous tape drives using tape cartridges, the head is positioned by directly driving the head with a follower nut positioned on a lead screw. This method, although simple and straightforward, limits the resolution of the head positioning as a function of the pitch of the lead screw. Hence, a stepper motor is required to have a very fine step increment for adequate positioning accuracy. In one commercial approach, a spiral surface cam, mounted to a stepper motor, uses a lever arm actuated by the cam surface to position the recording head. While this approach uses the mechanical advantage of the lever arm, the cam itself is only able to rotate one full revolution. Hence, a very precise cam with a fine step increment on the stepper motor is required to obtain adequate accuracy in the positioning of the tape head.
A related patent, U.S. Pat. No. 4,858,047, assigned to the present assignee, discloses a fine positioning system for a back-up tape drive using a lead screw and lever arm approach. This device uses a cantilevered lever arm connected to a head mounting unit which is slidable on a single post. The lever arm utilizes the mechanical advantage of a predetermined ratio to accurately position the tape head without requiring an expensive stepper motor or multiple stepper motors. However, the torsional moments of the lever arm and head mounting unit create tracking errors in the operation of the device. Also, azimuth adjustment is still needed to accurately align the device.
There still exists a need for a tape head positioning system in a back-up tape drive which will reduce the torsional moments on the lever arm and the tape head mounting unit in the positioning system and eliminate the need for azimuth adjustment. The desired system would maximize precision positioning of the tape head while minimizing the expense of doing so.
3. Solution to the Problem
The present invention provides a solution to the problem by obtaining improved accurate positioning of the head through use of a follower nut mounted on a fine pitch lead screw with a lever arm mounted on the follower nut. The lever arm is mounted on the follower nut such that it eliminates cantilevered loads on the follower nut and substantially reduces the wobble effects created by lead screw run out. This mounting provides axial loading of the lever arm on the follower nut.
The present invention further provides a tape head mounting unit designed to reduce the torsional moments from movement of the tape head mounting unit.
The present invention also provides a positioning system that does not require azimuth adjustment.